1. Field of the Invention
The present invention relates to a method for manufacturing an electronic part, especially an electronic part that is formed by laminating ceramic layers, which is exemplified by a so-called multilayer ceramic electronic part. The present invention also relates to a method for manufacturing a so-called ceramic green sheet used in the aforementioned method. Examples of the multilayer ceramic electronic part mentioned here include multilayer ceramic capacitors, multilayer ceramic inductors, LC composite parts including capacitors and inductors formed therein, or EMC related parts etc.
2. Related Background Art
In recent years, with downsizing and rapid popularization of electronic apparatuses represented by cellular phones, an increase in mounting density of the electronic parts used for those apparatuses and improvement in their performance are required. Especially, demands for downsizing, decrease in thickness, increase in the number of layers and uniformization of each layer are placed on multilayer ceramic electronic parts that are used as passive elements in order to meet the above requirements. In addition, development of the manufacturing method that can meet those requirements is also demanded.
So called metal-ceramic combined baking, disclosed in, for example. Japanese Patent Application Laid-Open No. 2001-110662 and Japanese Patent Application Laid-Open No. 2001-85264, is a conventional manufacturing method used for manufacturing the aforementioned multilayer ceramic electronic parts exemplified by multilayer ceramic capacitors having electrodes formed in the interior thereof, which can meet the aforementioned requirements. Here, this metal-ceramic combined baking technology will be described briefly. In this technology, a plurality of electrodes are formed on a so-called ceramic green sheet at the same time using an electrically conductive paste composed of a metal powder and an organic binder material.
Subsequently, a plurality of simple ceramic green sheets and ceramic green sheets on which electrodes have been formed etc. are stacked to form a ceramic multilayer member. The electrodes will constitute the internal electrodes of a multilayer ceramic electronic part when it is finished. In addition, the ceramic multilayer member is pressed in its thickness direction so that the green sheets will be brought into close contact with each other. The multilayer member brought into close contact is cut into a certain size and separated so as to be subjected to baking. On the outer surface of the baked member thus obtained, external electrodes are form fitted. Thus, a multilayer ceramic electronic part is obtained.
In recent years, further downsizing and thickness reduction of the aforementioned multilayer ceramic electronic parts have been required, and it is necessary to reduce the thickness of dielectric layers made of a ceramic or the like sandwiched between internal electrodes. Therefore, it is required to perform the above-described process while further reducing the thickness of ceramic green sheets that constitutes the ceramic multilayer member. In view of these requirements, the thickness of the thinnest ceramic green sheet presently used is about 2 to 3 μm. In addition, the thickness of electrodes printed on the ceramic green sheets is about 1.5 to 2.0 μm.
The thickness of the ceramic green sheets and the electrodes formed on the surface thereof, the width and pattern shape of the electrodes, are substantially determined at the time when they are formed, and it is practically impossible to add a process of shaping them after they are formed. Conventionally, the electrodes or the like are formed by screen printing. In the screen printing, variations in the thickness in the formed area is ±10 to 20%, and the limit value of the pattern width that can be formed is considered to be about 50 μm. As disclosed in Japanese Patent Application Laid-Open No. 2002-184648, on the surface of a sheet produced by the screen printing, there is unevenness like an impression of a mesh. In view of this, a new production method is required to be devised in order to produce sheets having improved uniformity in thickness and improved surface evenness.
As one solution, there has been proposed a technology in which a sheet or layer having a desired thickness is formed by a ceramic slurry having photosensitivity or an electrode paste having photosensitivity, so that they are subjected to exposure and development processing to produce electrodes or the like with high accuracy in terms of width and shape etc. With that method it is possible to make the pattern width thinner and the positional accuracy of pattern formation can also be enhanced as compared to the printing process. However, in the case that the layer to be exposed is formed by a printing process, there will be the aforementioned unevenness of the layer surface, and the unevenness will remain unchanged even when ordinary exposure and development processing has been applied.
It may be possible to reduce the unevenness by applying mechanical processing such as pressing to the sheet or the layer after the sheet or the layer is formed. However, this is not desirable because the process will be lengthy. A method using a coater or spin coating process is another method for forming a sheet or a layer having no or reduced unevenness. However, on the surface of the layer obtained by the aforementioned coating process, there remains traces of a blade or the like and the variations in the thickness is ±3 to 5%, which still remains after the exposure and development processing. Therefore, in order to manufacture electronic parts having improved characteristics an improvement in the surface evenness or reduction of the variations in the thickness is required.
In the case that metal paste is applied on a base member by screen printing or using a coater to form an electrode layer, sag of the edge portion of the electrode or deterioration in straightness of the edge portion can occur depending on conditions such as viscosity of the metal paste etc. In addition, a run-over or faded portion can be generated upon application of slurry, which can cause short-circuit or conduction failure when assembled into an electronic part. Furthermore, upon reducing the coating thickness, there is the lower limit of the thickness of the coating that can be formed depending on various condition such as viscosity. Furthermore, it is difficult to reduce variations in the dimension in the thickness direction down to less than a few percent. This is also the case when a ceramic green sheet is produced using a ceramic slurry.
In the case of a ceramic green sheet that is used for forming an electronic part in the form of an inductor, a penetrating electrode or the like may be formed in some cases. In that case, it is desirable that the length of the penetrating electrode (or the thickness of the electrode) be controlled precisely in order to make electric characteristics of the inductor definite. However, at present, the thickness of the electrode is determined in accordance with the thickness of the ceramic sheet and it is practically difficult to control the thickness of the electrode independently from the thickness of the ceramic green sheet, as will be seen from Japanese Patent Application Laid-Open No. 2003-48303.
In addition, when for example an inductor or the like is to be manufactured, it is necessary to pattern an electrode or other parts into a complicated shape with respect to a planer direction. Screen printing can attain accuracy in the complex patterning to some extent. However, it is difficult to further improve the characteristics of an electronic part by using screen printing. In addition, it is considered difficult as described above to form the cross section of the electrode or other parts in a desired shape.
Furthermore, when for example inductors or the like are to be manufactured, it is preferable to use a ceramic green sheet having a pattern electrode and a penetrating electrode in the same single sheet from the viewpoint of accuracy of lamination and downsizing or the parts. In this case, from the viewpoint of reduction of the number of the process steps and enhancement of characteristics of the inductors, it is considered preferable, if possible, to form concavities and convexities in a partial area of a layer made of an insulator and to fill the multiple concavities with an electrode paste to form a pattern electrode and a penetrating electrode. However, it is difficult for conventional technologies to form such concavities and convexities with a high degree of accuracy.